The sense or nonsense of mobile-bearing total knee prostheses
Wolterbeek, N.
Citation
Wolterbeek, N. (2011, November 10). The sense or nonsense of mobile- bearing total knee prostheses. Retrieved from
https://hdl.handle.net/1887/18058
Version: Corrected Publisher’s Version
License: Licence agreement concerning inclusion of doctoral thesis in the Institutional Repository of the University of Leiden
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Summary
The focus of this thesis was if the in vivo kinematics of total knee prostheses was consistent with the kinematics intended by design and to determine the additional value of insert mobility and thus ‘the sense or nonsense’ of mobile-bearing knee prostheses. The added value of this thesis to the current literature is the integration of different measurement techniques. Fluoroscopy is combined with RSA and motion analysis techniques to fully understand the in vivo knee kinematics beyond which can be obtained by either technique alone. Results demonstrate that the integration of different measurement techniques was indeed of great value to comprehend the in vivoknee kinematics.
Knowledge of the muscular control of knee prosthesis provides insight into the integration of the prosthesis within the musculo-skeletal system. After total knee arthroplasty, rheumatoid arthritis patients showed lower net knee joint moment and higher co-contraction than healthy controls indicating avoidance of net joint load and an active stabilization of the knee joint (Chapter 3). Anticipatory stabilization and co- activation are mechanisms to protect the soft tissue from external loads by increasing the stiffness of the knee. However, moving with excessive muscle activations and co-activations is inefficient and large forces are transmitted to the bone-implant interface which could lead to micromotion of the tibial component (Chapter 4).
Muscle activation did not change in the first two post-operative years (Chapter 5 and 6). Therefore, to prevent problems caused by excessive muscle activations and co-activations, rehabilitation programs for patients with total knee prostheses should include besides muscle strength training, elements of muscle-coordination training.
Summary
High congruency between the insert and the femoral component in combination with free rotation of the mobile insert is assumed to be beneficent for the longevity of the prosthesis by reducing multidirectional wear on the femoral aspect of the insert and friction at the bone-implant interface. However, high congruency of the insert seems to lead to undesired restrictions of motions of the femoral component which in turn might be a disadvantage for the functioning and long-term survival of that specific total knee prosthesis design (Chapter 4 and 5).
Furthermore, high congruency does not guarantee adequate insert rotation.
Reversed and divergent axial rotations with increasing knee flexion were seen in patients with the ROCC total knee prosthesis. The single-radius Triathlon total knee prosthesis including a less congruent insert showed preferable axial rotation of the insert compared to that of the high congruent ROCC total knee prosthesis (Chapter 4, 5, 7, 8). Based on these results, an optimal level of congruency between the insert and femoral component should be found.
Early migration in 33% of the mobile-bearing group versus 9% in the fixed-bearing group indicates that early migration of the tibial component is worse in the mobile- bearing group. It implies that the mobile insert does not improve initial fixation of the prosthesis to the bone, as intended by mobile-bearing designs (Chapter 7). Despite the mobile insert was following the femoral component during motion, and therefore performed as intended, no kinematic advantages of the mobile-bearing total knee prosthesis were seen.
In vivokinematics of most included total knee prostheses were consistent with the kinematics intended by their design (Chapter 8). However, some prostheses showed reversed or paradoxical kinematics in some parts of their functional range of motion.
At the current time there is no compelling reason for the widespread use of mobile- bearing total knee prostheses over successful fixed-bearing total knee prostheses either in terms of improved kinematics, early migration, clinical and radiological success.
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